Systems and methods for using adaptive coding and modulation in a regenerative satellite communication system

ABSTRACT

Techniques are described for implementing adaptive coding and modulation (ACM) in regenerative satellite systems to adapt the modulation and/or FEC coding of transmitted waveforms to the conditions of the link. In a first implementation, ACM is implemented on an uplink from a terminal to a regenerative satellite. In this implementation, an uplink modulation and coding combination (ModCod) is estimated by the transmitting terminal based on the quality of signals received from the regenerative satellite on the downlink. In a second implementation, ACM may be implemented on a downlink from a regenerative satellite to a terminal. In this implementation, a transmit terminal may insert a field in a transmitted packet header that indicates a downlink ModCod to be used by the regenerative satellite when transmitting packets to a receiving terminal. The regenerative satellite may reencode and remodulate the packet using the ModCod indicated in the field of the packet header.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of U.S.patent application Ser. No. 15/281,737 filed on Sep. 30, 2016.

TECHNICAL FIELD

The present disclosure relates generally to satellite networks. Moreparticularly, some embodiments of the present disclosure are directedtoward systems and methods for using adaptive coding and modulation in aregenerative satellite communication system.

BACKGROUND

Modern satellite communication systems provide a robust and reliableinfrastructure to distribute voice, data, and video signals for globalexchange and broadcast of information. These satellite communicationsystems have emerged as a viable option to terrestrial communicationsystems for carrying data traffic such as Internet traffic. A typicalsatellite Internet system comprises subscriber terminals, a satellite, aground station, and connectivity to the internet. Communication in sucha system occurs along two paths: 1) a forward path comprising an uplinkfrom a subscriber terminal to the satellite to a downlink to the groundstation to the internet; and 2) a return path comprising a path from theinternet to the ground station to an uplink to the satellite to adownlink to the subscriber terminal.

Adaptive coding and modulation (ACM) is a technique used in somesatellite systems to adapt the modulation and/or forward errorcorrection (FEC) coding of the transmitted waveform to the conditions ofthe link as appropriate for each receiving terminal. Per-terminal linkconditions might be affected by substantially static factors such asantenna pointing accuracy of a transmitting or receiving terminal, aswell as by dynamic factors such as changing weather attenuationaffecting uplink or downlink propagation. The objective of ACM is tomeet a target receive signal quality at the destination of thecommunication path (e.g., bit error rate, packet loss rate, or othermetric) while maximizing link capacity (e.g., bits/symbol orbits/Hertz).

ACM might be used to optimize a point-to-point communication link, suchas from a terminal transmitting an uplink carrier, through atransponded, bent-pipe, satellite, to a terminal receiving thetransponded carrier on the downlink. ACM may also be used to optimizepoint-to-multipoint links, such as an uplink carrier transmitted througha bent pipe satellite to a set of receivers within the same downlinkspot beam, onto which carrier are multiplexed data packets each destinedto one or more of the several receiving terminals.

To date, ACM techniques have not been applied in regenerative satellitesystems. In a regenerative satellite system, the satellite itself hasdigital processing hardware. This provides several advantages. First,the regenerative satellite demodulates, decodes, encodes, andremodulates the digital uplink signal to form a downlink signal. Thisprovides separation of the uplink from downlink by regenerating thedigital signal and can save in the link budget's signal strength.Second, this digital on-board processing permits the satellite to takethe data packets it receives on the uplink and route or switch it toparticular downlink locations. Additionally, satellite demodulators onthe uplink may be assigned to particular uplink spotbeams to listen toassigned uplink frequencies, i.e., uplink sub-bands. The satellite'suplink antennas and demodulators are able to separate and differentiatesignals from satellite terminals transmitting from these uplink spotbeams. This allows reuse of a same frequency in different uplinks,providing a major increase in frequency efficiency.

SUMMARY

Techniques are described for implementing ACM in regenerative satellitesystems to adapt the modulation and/or FEC coding of transmittedwaveforms to the conditions of the uplink or downlink.

In a first embodiment, ACM may be implemented on an uplink from aterminal to a regenerative satellite. In this embodiment, a terminaltransmitting on an uplink may include: a receiver configured to receivea signal on a downlink from a regenerative satellite; a module fordetermining a quality of the received signal; a module for determiningan uplink modulation and coding combination (ModCod) for uplinktransmissions to the regenerative satellite based on the determinedquality of the signal; and a transmitter configured to transmit a signalon an uplink to the regenerative satellite, where the signal transmittedon the uplink is modulated and encoded based on the determined ModCod.

The transmitting terminal may be at least one of a gateway, a hub, andan earth station. Alternatively, the transmitting terminal may be a verysmall aperture terminal (VSAT). In implementations, the uplink ModCod isdetermined by mapping, using a table, the determined quality of thereceived signal to the uplink ModCod. For example, a received signalratio of mean energy per symbol to noise power spectral density(E_(s)N₀) may be mapped to the uplink ModCod.

In a second embodiment, ACM may be implemented on a downlink from aregenerative satellite to a terminal. In this embodiment, a transmittingterminal may receive from a receiving terminal, at least one of adownlink modulation and coding combination (ModCod) and receive signalmetrics. In response to receiving the at least one of a downlink ModCodand receive signal metrics, the transmitting terminal may insert into aheader of a packet a field indicating a downlink ModCod to be used by aregenerative satellite when transmitting on a downlink to the receivingterminal; and transmit on an uplink, the packet to a regenerativesatellite. In one implementation, the transmitting terminal receives thedownlink ModCod from the receiving terminal and updates a tableindicating a downlink ModCod for the receiving terminal. In anotherimplementation, the transmitting terminal receives the receive signalmetrics and maps the receive signal metrics to the downlink ModCod. Thereceive signal metrics may include an E_(s)N₀.

In implementing ACM on a downlink, a regenerative satellite system mayinclude a regenerative satellite that includes: a receiver configured toreceive a signal; circuitry for demodulating and decoding the receivedsignal to obtain a packet; circuitry for reading, from a header of thepacket, a field indicating a downlink modulation and coding combination(ModCod) to be used when transmitting on a downlink to a receivingterminal that is a destination of the packet; and circuitry formodulating and encoding the packet at the regenerative satellite basedon the indicated downlink ModCod. In one implementation, theregenerative satellite receives the signal on an uplink from atransmitting terminal transmitting to the receiving terminal. In anotherimplementation, the regenerative satellite receives the signal from asecond regenerative satellite connected to the regenerative satelliteover an inter satellite link.

In implementations, the regenerative satellite system includes one ormore regenerative satellites connected to the regenerative satelliteover inter satellite links. The regenerative satellites may be inelliptical orbit or in low earth orbit. In such implementations, theregenerative satellite may include a packet switch for determining if adestination downlink of a received packet is a downlink of a differentsatellite.

In a third embodiment, ACM may be implemented by a regenerative highaltitude platform system on a downlink or uplink by applying the samemethods disclosed herein for implementing ACM in a regenerativesatellite system. The regenerative high altitude platform may compriseone or more aircrafts or one or more balloons.

Other features and aspects of the disclosure will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresin accordance with various embodiments. The summary is not intended tolimit the scope of the invention, which is defined solely by the claimsattached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The technology disclosed herein, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments of the disclosedtechnology. These drawings are provided to facilitate the reader'sunderstanding of the disclosed technology and shall not be consideredlimiting of the breadth, scope, or applicability thereof. It should benoted that for clarity and ease of illustration these drawings are notnecessarily made to scale.

FIG. 1 illustrates a transponded satellite system 100 using ACM forpoint-to-point links between terminals.

FIG. 2 is a block diagram illustrating an example operation of a trafficand control processing module for a terminal of the transpondedsatellite system of FIG. 1.

FIG. 3 is a block diagram illustrating an example operation of areceiver link adaptation module for traffic and control processingmodule of FIG. 2.

FIG. 4 illustrates an example ACM trajectory table that may beimplemented by the RX link adaptation module of FIG. 3 to determine whatModCod best meets a receive quality objective.

FIG. 5 illustrates an example transponded satellite system using ACM forpoint-to-multi-point links from a satellite gateway to terminals and forpoint-to-point links from terminals to the satellite gateway.

FIG. 6 is a block diagram illustrating an example operation of a trafficand control processing module for a terminal of the transpondedsatellite system of FIG. 5.

FIG. 7 is a block diagram illustrating an example operation of atransmitter link adaptation module that determines, based on a qualitymetric received from a gateway, at which ModCod to encode and transmitpackets to the gateway.

FIG. 8 illustrates a multi-satellite regenerative satellite system inaccordance with the technology disclosed herein.

FIG. 9 illustrates an example payload of a regenerative satellite ofFIG. 8 in accordance with embodiments of the technology disclosedherein.

FIG. 10 is an operational flow diagram illustrating an example methodthat may be implemented to provide ACM on the uplink from a terminal toa satellite in a regenerative satellite communication system.

FIG. 11 is an operational flow diagram illustrating an example methodthat may be implemented to provide ACM on the downlink from a satelliteto a terminal in a regenerative satellite communication system.

FIG. 12 illustrates an example packet header enabling end-end downlinkACM control of ModCod selection for a regenerative satellitecommunication system.

FIG. 13 is an operational flow diagram illustrating an example methodthat may be implemented by a regenerative satellite to provide ACM onthe downlink.

FIG. 14 is a block diagram illustrating an example operation of atraffic and control processing module for a terminal of the regenerativesatellite system of FIG. 8.

FIG. 15 is a block diagram illustrating an example operation of atransmitter link adaptation module of a terminal of the regenerativesatellite system of FIG. 8.

FIG. 16 illustrates an example destination downlink ModCod table thatmay be implemented by the transmitter link adaptation module of FIG. 15.

FIG. 17 illustrates an example computing module that may be used inimplementing features of various embodiments.

FIG. 18 illustrates an example chip set that can be utilized inimplementing architectures and methods for dynamic bandwidth allocationin accordance with various embodiments.

The figures are not intended to be exhaustive or to limit the inventionto the precise form disclosed. It should be understood that theinvention can be practiced with modification and alteration, and thatthe disclosed technology be limited only by the claims and theequivalents thereof.

DETAILED DESCRIPTION

Various embodiments of the systems and methods disclosed herein providetechniques for implementing ACM in regenerative satellite systems toadapt the modulation and/or forward error correction (FEC) coding oftransmitted waveforms to the conditions of the link.

In a first implementation, systems and methods are described forimplementing ACM on an uplink from a terminal to a regenerativesatellite. In this implementation, an uplink modulation and codingcombination (ModCod) is estimated by the transmitting terminal based onthe quality of signals received from the regenerative satellite on thedownlink. This simplified uplink ModCod determination may be viablebecause the downlink and uplink between a given terminal and a givenregenerative satellite go through the same propagation path and weather.By estimating the uplink ModCod at the transmitting terminal instead ofthe regenerative satellite, the regenerative satellite's hardware andsoftware requirements are kept to a minimum, thereby avoiding the riskand expense of implementing this function in space.

In a second implementation, ACM may be implemented on a downlink from aregenerative satellite to a terminal. In this implementation, a transmitterminal may insert a field in a transmitted packet header thatindicates a downlink ModCod to be used by the regenerative satellitewhen transmitting packets to a receiving terminal. On the downlink, theregenerative satellite may remodulate and reencode the packet using theModCod indicated in the field of the packet header. By not requiring theregenerative satellite to determine and keep track of a downlink ModCodfor each receiving terminal, the regenerative satellite's hardware andsoftware requirements are again kept to a minimum.

Before describing in detail the disclosed systems and methods forimplementing ACM in regenerative satellite systems, it is instructive todescribe the use of ACM in transponded satellite systems, wheresatellites function as analog transponders that take uplink frequenciesand shift them to their downlink frequencies in a bent-pipe fashion.FIGS. 1-7 illustrate implementations of ACM in transponded satellitesystems.

FIG. 1 illustrates an example transponded satellite system 100 using ACMfor point-to-point links between terminals. In this example, transpondedsatellite 130 provides a point-to-point link between terminal 1 andterminal 2, each of which are capable of ACM through connectedtransponded satellite 130. Each of terminal 1 and 2 may comprise areceiver physical layer (Rx PHY) 122, a receiver media accesscontrol/satellite link control module (Rx MAC/SLC) 124, a transmitterphysical layer (Tx PHY) 121, a Tx MAC/SLC 123, and a traffic and controlprocessing module 130. It should be noted that one of ordinary skill inthe art will understand how other transmitter or receiver configurationscan be implemented in each terminal, and that one or more of aterminal's components can be implemented in either digital form (e.g.,as software running on a DSP or other processing device, with theaddition of a DAC) or as analog components.

On the transmitter side, Tx PHY 121 may perform functions such asencoding, interleaving, modulation, and filtering, and Tx MAC/SLC 123may perform functions such as scheduling, packet segmentation, andencryption. On the receiver side, Rx PHY 122 may perform functions suchas radio frequency (RF) filtering, demodulation, deinterleaving,decoding, and receive signal quality measurement, and Rx MAC/SLC 124 mayperform functions such as packet reassembly and decryption. Traffic andcontrol processing module 130, further described below, may providefunctions such as system management, user traffic management andcontrol, and link adaptation.

During operation, terminal 1 may transmit on uplink 105A a firstwaveform carrying a packet at some ModCod. For example, the code may beany one of FEC codes 1/2, 2/3, 3/4, 5/6, 7/8, 8/9, 9/10, etc., and themodulation format may be any one of Amplitude Phase Shift Keying (APSK),Quadrature Phase Shift Keying (QPSK), n/M-MPSK, other orders of MultiplePhase Shift Keying MPSK, Quadrature Amplitude Modulation (QAM), and soon. In a particular implementation, the ModCod may be selected inaccordance with the Digital Video Broadcasting-Satellite secondgeneration (DVB-S2) standard. In implementations, a default robustModCod is used during initial operation to prevent packet loss.

On the downlink 105B, receiving terminal 2 receives and processes thefirst waveform carrying the packet transmitted by terminal 1.Additionally, receiving terminal 2 measures one or more receive qualitymetrics (e.g., the ratio of mean energy per symbol to noise powerspectral density (E_(s)N₀)), which can be used by system 100 todetermine an appropriate ModCod to be used by transmitting terminal 1.Based on the one or more receive quality metrics, terminal 2 maygenerate a packet to request a ModCod change of terminal 1 to meet atarget quality threshold. In one embodiment, the request for the ModCodchange may be transmitted over uplink 106A using a second waveform,encoded using the last terminal 1 requested ModCod. Alternatively, therequest may be transmitted as a part of a regularly scheduled traffic orcontrol packet. After receiving the requested ModCod change overdownlink 106B, terminal 1 may use the indicated ModCod for futuretransmissions to receiving terminal 2, until a new ModCod is indicated,or unless the transmitting terminal has not received communication fromthe receiving terminal (i.e., traffic or signaling in the oppositedirection) for some period of time.

It should be noted that although the ModCod determination in thisexample implementation is made by the receiving terminal, in alternativeimplementations the ModCod determination may be made by the transmittingterminal or a control system based on quality metrics signaled by thereceiving terminal.

By way of example, when a transmission path is experiencing some weatherattenuation on the uplink to satellite 130 or the downlink fromsatellite 130, ACM link adaptation might cause a robust ModCod providingrelatively high link margin to be used, such as QPSK modulation withrate 3/4 FEC coding, providing 1.5 bits/symbol of traffic carryingcapacity and 0.5 bits/symbol of FEC coding. As the weather improves andattenuation lessens, ACM link adaptation might cause a less robustModCod to be used, such as 8PSK modulation with rate 3/4 FEC coding,providing 2.25 bits/symbol of traffic carrying capacity and 0.75bits/symbol of FEC coding. As the weather further improves, the ModCodmight be adapted to 8PSK with rate 9/10 FEC, providing 2.7 bits/symbolof traffic carrying capacity and 0.3 bits/symbol of FEC coding. In thismanner, link traffic capacity is dynamically adapted to link quality asmeasured by the receiver.

FIG. 2 is a block diagram illustrating an example operation of a trafficand control processing module 130 for a terminal of the transpondedsatellite system of FIG. 1. During operation, Tx link adaptation module200 may track the most recent ModCod request by its peer terminal (e.g.,terminal 1 may track the most recent ModCod requested by terminal 2) andsignal Tx MAC/SLC 121 to use that ModCod for each transmit packet. Inthis example, Rx MAC/SLC 122 of terminal 1 may process packets receivedfrom terminal 2, and forward these packets to an Rx Relay module 250.

Depending on the type of packet, Rx Relay module 250 may forward atraffic packet to a Traffic Processing module, a management or controlpacket to a Mgt/Control Processing module, and a requested return ModCodpacket, containing request from terminal 2 that terminal 1 transmitfuture packets to terminal 2 using a particular desired ModCod, to a TxLink Adaptation module 200. Other packet types and modules may exist andbe supported by Rx Relay module 250. The Tx Link Adaptation module 200may extract the desired ModCod from the requested return ModCod packet,save it for later use, and indicate to Tx MAC/SLC 121 to use the savedModCod with each subsequent packet to be transmitted to terminal 2.Alternatively, if the requested return ModCod is included within theheader of a traffic packet rather than being sent in a separate packet,Rx Relay module 250 may send the traffic packet to the TrafficProcessing module, and copy the requested ModCod from the packet headerand send it to the Tx Link Adaptation module 200.

Also shown in FIG. 2, Rx MAC/SLC 122 may send a receive quality metric(e.g., an E_(s)N₀ measurement) associated with a received waveformcontaining a packet, to Rx Relay module 250 to be forwarded to the Rxlink adaptation module 300. The Rx link adaptation module 300 maydetermine what ModCod best meets a receive quality objective, andgenerate a ModCod request to send to its peer terminal when a change isrequired. The Rx link adaptation module 300 may send that request to aTx Packet Mux, either as a packet to be inserted into the packet streamto be transmitted via the Tx Link Adaptation Module 200 and Tx MAC/SLC121, or as a value to be inserted by the Tx Packet Mux into the headerof some other traffic or control packet destined to the peer terminal 2.

FIG. 3 is a block diagram illustrating an example operation of RX linkadaptation module 300. FIG. 3 will be described concurrently with FIG.4, which illustrates an example ACM trajectory table 400 that may beimplemented by RX link adaptation module 300 to determine what ModCodbest meets a receive quality objective. As illustrated, RX linkadaptation module 300 may comprise a quality short term filter 340, anACM control 350, and an ACM trajectory table 400. Filter 340 may providehysteresis such that atmospheric and propagation transients that affectthe receive waveform only momentarily do not trigger changes (e.g., arequest to change ModCod).

ACM Control 350 may receive ACM ModCod ingress/egress thresholds fromACM trajectory table 400 to determine when to transition (up or down)between ModCod options, either to add more coding and/or changemodulation to overcome link degradation, or to reduce coding and/orchange modulation when degradation lessens. As illustrated by thisexample, ACM control 350 may cause periodic transmission of a ModCodrequest until the terminal obtains a desired signal quality.

ACM trajectory table 400 may specify a ModCod number or ID correspondingto a particular ModCod, an entry threshold indicating when to go up to aModCod, and an exit threshold indicating when to go down to a lowerModCod. As illustrated in this embodiment, an E_(s)N₀ metric is used todetermine when to transition between different ModCods. However, aswould be appreciated by one having skill in the art, other metrics maybe used to make the transition.

By way of example, consider a receiving terminal currently receivingwaveforms at ModCod No. 5 (i.e., QPSK 3/5) with an E_(s)N₀ of 3.5decibels (dB). If the terminal's E_(s)N₀ as filtered by short termfilter 340 reaches or exceeds 4.1 dB, it may signal to go up from ModCod5 to ModCod 6 (i.e., QPSK 2/3). As another example, the terminal wouldsignal to drop down from ModCod 6 to ModCod 5 when its E_(s)N₀ asfiltered by short term filter 340 drops to 3.7 dB or below.

FIG. 5 illustrates an example transponded satellite system 500 using ACMfor point-to-multi-point links from a satellite gateway 510 to terminals520-530 and for point-to-point links from terminals to a satellitegateway. In this example configuration, gateway 510 transmits a carrierthat is received by multiple terminals (e.g., terminals 520-530) in asatellite spot beam of satellite 540. The transmitted carrier carriesmultiplexed packets destined for the receiving terminals (e.g.,terminals 520-530).

For each terminal, gateway 510 may use a ModCod requested by theterminal, such that a common transmit carrier may include codeblocks atdifferent ModCods. For example, the gateway transmitter may multiplexQPSK 3/4, 8PSK 3/4 and 8PSK 9/10 code blocks onto the same transmitcarrier, if those are the ModCods determined to be appropriate for theintended receiving terminals for the packets contained within those codeblocks. In implementations, the gateway may use a more robust ModCodthan had been determined for a given receiving terminal, if that allowsmore efficient packing of packets destined to multiple receivingterminals into a single code block. In case of multicast traffic, i.e.,data packets intended for multiple receiving terminals, the gateway mayuse a default ModCod, or may use the most robust ModCod required by anyof the intended receiving terminals.

In example system 500, the traffic and control processing module 550 ofgateway 510 maintains a database 545 that tracks the latest ModCodrequested by each terminal. During operation, the database may beupdated with each terminal ModCod request, and the appropriate ModCodentry for each packet to be sent to a terminal may be looked up prior totransmission.

In this implementation, the TX MAC/SLC 523 of gateway 510 may alsoorganize code rates to schedule packets destined to the differentterminals in to required code blocks. For example, packets or parts ofpackets to different terminals may be fitted into the same code block ifthe requested ModCods are consistent, or to fill out free space in amore robust code block. The RX PHY 122 and RX MAC/SLC 524 of gateway 510may receive carriers (e.g., continuous or time division multiple access(TDMA) bursts) from the multiple terminals, and measure receive qualitymetrics to be returned to each respective terminal so that the terminalmay control its own transmit ModCods.

FIG. 6 is a block diagram illustrating an example operation of a trafficand control processing module 600 for a terminal (e.g., terminal 520 or530) of transponded satellite system 500. In this implementation, ratherthan a peer terminal requesting a ModCod to be used by the terminal forits transmission, gateway 510 sends a receive quality metric, and Txlink adaptation module 700 determines, based on the quality metricreceived from the gateway, at which ModCod to transmit. Additionally,similar to receive link adaptation module 300, receive link adaptationmodule 650 determines ModCod transitions and triggers ModCod requests.Accordingly, as illustrated below, each terminal has ACM trajectorytables to control both the forward (gateway to terminal) and return(terminal to gateway) ACM operation.

FIG. 7 is a block diagram illustrating an example operation oftransmitter link adaptation module 700 that determines, based on aquality metric received from a gateway, at which ModCod to encode andtransmit packets to the gateway. As illustrated, transmitter linkadaptation module 700 may comprise a gateway receiver quality short termfilter 710, a transmitter ACM control 720, a transmitter ACM trajectorytable 730, and a transmitter relay module 740. During operation,transmitter ACM trajectory table 730 is used by transmitter ACM control720 to determine at which ModCod packets are encoded to the gateway.After a transmit ModCod 725 is selected, transmit relay module 740indicates the selected ModCod 725 with each packet sent to Tx MAC/SLC121.

FIG. 8 illustrates a multi-satellite regenerative satellite system 800in accordance with the present disclosure. In example system 800,regenerative satellites 810 a-810 c may provide one or more spot beamsto terminals 820 on the downlink, and receive communications fromterminals 820 on the uplink. As will be further described below, eachregenerative satellite 810 a-810 c may demodulate and decode uplinkcarriers to extract conveyed data packets according to some uplinkwaveform, route those packets to downlink spot beams or throughinter-satellite links, and modulate and encode downlink packetsaccording to some downlink waveform. Additionally, as will be furtherdescribed below, ACM may be provided on the uplink to and downlink fromregenerative satellites 810 a-810 c.

Terminals 820 may comprise a very small aperture terminal (VSAT), agateway, a hub, or an earth station. For example, terminals 820 can beVSATs and may connect to the Internet through satellites 810 a-810 c. Aterminal may be used at a residence or place of business to provide auser with access to the Internet. VSATs or Mobile Satellite Terminals(MSTs), may be used by users to access the satellite network, and mayinclude a remote satellite dish for receiving RF signals from andtransmitting RF signals to satellites 810-810 c, as well as a satellitemodem and other equipment for managing the sending and receiving ofdata. They may also include one or more remote hosts, which may becomputer systems or other electronic devices capable of networkcommunications at a site.

Regenerative satellites 810 a-810 c may be placed in a geosynchronousearth orbit (GEO), low earth orbit (LEO), elliptical orbit, or someother configuration. The satellites may operate in the Ka-band, Ku-band,C-band or other suitable band. Signals passing through satellites 810a-810 c may be based, for example, on the DVB-S2 standard (ETSI EN 302307) using signal constellations up to and including at least 32-APSK,or on the Internet Protocol over Satellite (IPoS) standard (ETSI TS 102354), or on other standard or proprietary specifications incorporatingACM. Other suitable signal types may also be used, including, forexample higher data rate variations of DVB-S2, or DVB-S2 extensions oradaptations sometimes designated as DVB-S2X. Also illustrated by FIG. 8are inter-satellite links (ISLs) between regenerative satellites 810a-810 c. As will further described below, ACM control may be appliedend-to-end across multiple ISLs.

FIG. 9 illustrates an example payload 900 for a regenerative satellite810 a-810 c in accordance with embodiments of the technology disclosedherein. FIG. 9 illustrates certain functional blocks that are relevantto the disclosed technology, but it should be noted that a given payloadmay include many other functional blocks, and the realization of theillustrated functions by specific hardware modules is not implied inthis diagram. It should also be noted that one of ordinary skill in theart will understand that one or more of the components of regenerativesatellite payload 900 may be implemented in digital form (e.g., assoftware running on a DSP or other processing device, with the additionof a DAC). In addition, certain components may be implemented in analogform (e.g., RF antenna).

On the uplink/receiver side, payload 900 may comprise an uplink (U/L) RFantenna 901 for receiving an uplink waveform, an U/L PHY 902, an U/LMAC/SLC 903, and an U/L packet processing module 904. U/L PHY 902 mayperform functions such as RF filtering, demodulation, deinterleaving,and decoding, and U/L MAC/SLC 903 may perform functions such as packetreassembly and decryption.

On the downlink/transmitter side, payload 900 may comprise downlink(D/L) packet priority queues 915, D/L scheduling/control module 914, DLMAC/SLC 913, D/L PHY 912, and D/L RF antenna 911 for transmitting adownlink waveform. D/L PHY 912 may perform functions such as encoding,interleaving, modulation, and filtering, and D/L MAC/SLC 913 may performfunctions such as scheduling, packet segmentation, and encryption.

Packet switch 920 may route packets received from other satellites overISLs and packets received over an uplink. For example, packets may bereceived from other satellites using ISL Rx packet processing module922, and packet switch 920 may determine (e.g., based on a destinationfield in the packet header) whether to transmit these packets on thedownlink or to route these packets to another satellite along an ISL. Ifpackets are routed to other satellites, they may be placed in ISL Txpacket priority queues 921 in preparation for transmission to othersatellites.

ACM on Uplink of Regenerative Satellite Communication System

As noted above, ACM may be provided on the uplink from regenerativesatellites 810 a-810 c. In one implementation of ACM on the uplink, theregenerative satellite might perform functions analogous to what areceiving terminal performs in a transponded satellite systemimplementing ACM (described above with reference to FIGS. 1-7),measuring receive signal metrics and conveying either those metrics oran appropriate ModCod to the transmitting terminal or control system.The transmitting terminal would thereby adapt its transmit ModCodaccording to the metrics or ModCod signaled by the satellite or controlsystem. Either of these methods may place a significant burden on thesatellite over and above providing a flexible demodulator capable ofreceiving the uplink ACM waveform. The satellite would have to measureand associate particular signal metrics with particular transmittingterminals, and generate downlink signals to convey each appropriatemetric or ModCod to each appropriate terminal, or else convey suchmetrics to some control system. The satellite would have to performthese functions at a rate consistent with uplink throughput, possiblyrequiring implementation of custom application specific integratedcircuits (ASICs) for processing speed. In order to reduce the downlinkcapacity overhead required to convey ACM signaling, the satellite mightkeep track of what feedback it last signaled to each transmittingterminal, and generate downlink ACM signaling only in case ofsignificant change, but this would require the satellite to keep trackof terminals and implement further control logic. An architectureplacing such complexity in space involves significant implementationcost, risk, and difficulty to make changes to correct or improvealgorithms after the satellite is launched. Consequently, a simpleralternative is desirable.

FIG. 10 is an operational flow diagram illustrating an example method1000 that may be implemented by a terminal to provide one suchalternative to implementing ACM on the uplink from a terminal to asatellite in a regenerative satellite communication system 800. Inmethod 1000, further described below, the uplink ModCod may be estimatedbased on a received signal quality. This simplified uplink ModCoddetermination may be viable because the downlink and uplink between agiven terminal and a given regenerative satellite go through the samepropagation path and weather.

At operation 1002, a terminal 820 receives a signal on a downlink from aregenerative satellite 810 a-810 c. At operation 1004, the quality ofthe received signal is determined. For example, the E_(s)N₀ of thereceived signal may be measured and passed through a short-term filterto provide hysteresis to smooth out transient variations.

At operation 1006, an uplink ModCod is determined based on the receivedsignal quality. In embodiments, the uplink ModCod may be determinedbased on a mapping that accounts for differences between the uplink anddownlink propagation paths, including factors such as, for example,satellite and terminal antenna performance and power amplifier size,operation of power control algorithms, differences between the uplinkand downlink waveforms, effective satellite downlink power, calibrationmeasurement points, and other factors. This mapping may be provided as atable mapping a given receive signal quality metric (e.g., a receivedE_(s)N₀) to a desired downlink receive ModCod and also to a similar ordifferent desired uplink transmit ModCod, as appropriate for therelationship of expected downlink and uplink propagation performance.This mapping table may be an extension of the exemplary table in FIG. 4,with the indicated entry and exit threshold values mapped to separatereceive and transmit ModCods. The relationship of downlink and uplinkpropagation performance may be determined according to knowledge ofsatellite and terminal configuration and performance, differencesbetween respective uplink and downlink waveforms, or other factors,including local calibration processes executed during installation or onsome other basis.

In one embodiment, the terminal may be configured with downlink anduplink ACM control tables, such that when the terminal receive signalquality maps in the downlink ACM control table to use of a downlinkModCod (e.g., QPSK 3/4), the signal quality maps in the uplink ACMcontrol table to use of an uplink ModCod (e.g., QPSK 1/2). Inimplementations of this embodiment, the same ModCod may or may not beused on the uplink and downlink, depending on the differences betweenthe uplink and downlink conditions noted above. It should also be notedthat the same waveform may or may not be used on the uplink anddownlink.

At operation 1008, prior to uplink transmission, the terminal encodesand modulates signals based on the determined ModCod. Inimplementations, the determination of the ModCod may adjust the currentmodulation scheme and/or FEC rate applied to signals transmitted on theuplink. At operation 1010, a signal, encoded and modulated with thedetermined ModCod, is transmitted on the uplink to the regenerativesatellite.

The disclosed uplink ACM method 1000 may provide a number of benefits.The regenerative satellite would not have to measure or provide signalquality feedback to transmitting terminals. The satellite would not berequired to keep track of specific terminals or convey specific metricsto specific terminals. Downlink capacity would not be consumed to conveyuplink signal metrics or ModCods. The satellite would require lesscomplex logic, and be less susceptible to risk of logic errors beingdetected after launch. The satellite might also require less hardwareand consequently have lower mass and power requirements. Additionally,in case of a LEO or elliptical orbit regenerative satelliteconstellation, the transmitting terminal may automatically update itsuplink ModCod in case of transition to a different satellite, uponmeasuring one or more receive signal quality metrics associated withdownlink transmission received from the new satellite.

ACM on Downlink of Regenerative Satellite Communication System

As noted above, ACM may be provided on the downlink from regenerativesatellites 810 a-810 c. In one implementation of ACM on the downlink,the regenerative satellite may perform functions analogous to what atransmitting terminal performs in a transponded satellite systemimplementing ACM (described above with reference to FIGS. 1-7),maintaining a mapping of specific ModCods to specific terminals,changing that mapping as new downlink receive quality metrics or ModCodsare signaled for those terminals, adapting the transmit waveform foreach given packet according to the ModCod determined for the terminal orterminals to which that traffic is destined, and using a default robustModCod in case a mapping is not available or is stale. This may involvesignificant complexity, risk, and added hardware or software on thesatellite over and above providing a flexible modulator capable oftransmitting a downlink ACM waveform. The satellite would have to beconfigured with or learn to maintain a database of terminals, keep trackof their associated ModCods, be capable to process terminal ACM feedbacksignaling to update the ModCod mapping database, and look up terminalsin the mapping database in real-time to identify the ModCod to be usedfor specific traffic. If required to optimize the ModCod for a downlinkmulticast transmission according to the intended receive terminals, thesatellite would be required to know which terminals are intended toreceive the multicast data and to find in its mapping database the worstcase ModCod required by any of those recipients. As noted above foruplink ACM, placing such complexity and cost in a satellite might beunsuitable, and an alternative may be desired.

FIG. 11 is an operational flow diagram illustrating an example method1100 that provides one such alternative to implementing ACM on thedownlink in a regenerative satellite communication system 800. Atoperation 1102, a receiving terminal transmits one or more receivesignal metrics or a desired downlink ModCod to a transmitting terminalfrom which the receiving terminal's receive packets originated over aregenerative satellite communication system. For example, the receivingterminal may send a QPSK 3/4 ModCod request to a terminal which hadtransmitted on its uplink the received downlink packet. Alternatively,for example, the terminal may send a filtered receive E_(s)N₀ value to aterminal which had transmitted on its uplink the received downlinkpacket, and such transmitting terminal may then map that E_(s)N₀ valueto a QPSK 3/4 ModCod value. Alternatively, the receiving terminal maysend a filtered signal metric, for example, E_(s)N₀ having been passedthrough a short term filter so as to smooth out transient variations,and the transmitting terminal may determine an appropriate downlinkModCod for the receiving terminal based on the received signal metric.

At operation 1104, in response to receiving the downlink ModCod (ordetermining the ModCod based on the received signal metrics), thetransmitting terminal inserts into each transmitted packet header afield indicating the downlink ModCod to be used by a regenerativesatellite when transmitting on the downlink to the receiving terminal.For example, the transmitting terminal may embed a QPSK 3/4 requestwithin each subsequent uplink packet destined to that same receivingterminal. In embodiments, the transmitting terminal may maintain andupdate a table of downlink ModCod mapping for each receiving terminalthat it transmits packets to. In other words, the table would be updatedeach time the transmitting terminal receives a request for a newdownlink ModCod from a receiving terminal. In implementations where theregenerative satellite system includes ISLs, the field indicating thedownlink ModCod may be used only by a last hop satellite (i.e., theregenerative satellite that transmits to the receiving terminal).

FIG. 12 illustrates an example packet header enabling end-end downlinkACM control of ModCod selection for a regenerative satellitecommunication system. As illustrated, the packet header may include,among other fields, a destination MAC address 1111 indicating to whichterminal or terminals the packet is destined, a destination location1112 indicating where the destined terminal is for routing purposes(e.g., location of a ground spot beam), a destination downlink ModCod1113 indicating a ModCod to be used by a last hop satellite for packettransmission, and a source downlink ModCod 1114 (e.g., if thetransmitting terminal informs the receiving terminal of its returnModCod request using a transmitted packet). Other fields in the packetheader may include a source MAC address (e.g., which terminal sent thepacket), a source location, a packet priority or drop class in case ofdownlink or ISL congestion, a time to live (TTL), a header checksum, apacket checksum, and the packet payload.

At operation 1106 a regenerative satellite adapts the downlink waveformaccording to the desired ModCod as indicated in each packet to betransmitted to the destination terminal. For example, the satellitecould extract and use an indicated QPSK 3/4 ModCod to regenerate asubsequent packet into the destination terminal downlink. As shown bythe example of FIG. 9, D/L scheduling and control module 914 may extractthe ModCod from the packet header and provide it to D/L MAC/SLC 913 foruse in code block construction and for encoding and modulation by D/LPHY 912.

In implementations where a given receiving terminal receives dataoriginating from multiple transmitting terminals, method 1100 may berepeated for each transmitting terminal. The receiving terminal maytransmit its desired ModCod (or receive signal metrics) to each suchtransmitting terminal, and each such transmitting terminal may embed theModCod request within each packet destined to the receiving terminal,such that the regenerative satellite uses the intended ModCod fordownlink transmissions to the receiving terminal.

By way of example, with reference to FIG. 8, if terminal 1 is incommunication with terminals 2, 3, 4, and 5, it may signal to each ofthose terminals what ModCod to indicate in the headers of packetsdestined to terminal 1, and when being sent by regenerative satellite 1that indicated ModCod would be used. Conversely, terminal 1 wouldsimilarly receive from terminals 2, 3, 4, and 5 the ModCods to be usedfor transmissions respectively to each of them. Terminal 1 couldmaintain a table of ModCod mapping for terminals 2, 3, 4, and 5, and usethe correct ModCod for each destination.

The disclosed downlink ACM method 1100 may provide a number of benefits.The satellite would not have to maintain a database of terminals andrequested ModCods, and would not have to update the database based onACM signaling. The satellite would require less complex logic, and beless susceptible to risk of logic errors being detected after launch.The satellite may also require less hardware and consequently have lowermass and power requirements.

In one embodiment, determination of the downlink ModCod most appropriatefor a receiving terminal may account for satellite movement (e.g., inthe case of regenerative LEO or elliptical satellite constellations). Asthe satellite moves and the distance to the terminal decreases orincreases, the satellite downlink may pass through different weather,and the terminal may transition across a satellite downlink spot beamand to another spot beam. The downlink ModCod adaptation may track thesechanges so long as the rate or schedule of ACM feedback from thereceiving terminal to the regenerative satellite or to the transmittingterminal or control system is sufficient. As a high feedback rate mayconsume capacity that could otherwise be used for traffic, the feedbackrate may be reduced based on factors such as, for example, the receivingterminal location, satellite beam pattern, satellite ephemeris, or somecombination thereof.

In another embodiment, determination of the downlink ModCod mostappropriate for a receiving terminal may account for the terminaltransitioning from one satellite to another (e.g., in the case ofregenerative LEO or elliptical satellite constellations). Duringsatellite transition, even if the terminal elevation angle to thearriving satellite is similar to the elevation angle for the departingsatellite, the downlink propagation path may pass through differentweather and experience different attenuation. In response, the downlinkModCod may be adapted to a robust ModCod upon transition. Inimplementations, satellite transitions may be anticipated based onknowledge of the terminal location and satellite ephemeris, and a switchto a robust ModCod may be made just prior to transition to the newsatellite, thereby minimizing the risk of packet loss. This may beachieved by the receiving terminal signaling a ModCod change ortransition event to each applicable transmitting terminal, a controlsystem, or to the regenerative satellite as appropriate, prior tochanging to a new satellite.

FIG. 13 is an operational flow diagram illustrating an example method1300 that may be implemented by a regenerative satellite to provide ACMon the downlink. Method 1300 will be described in conjunction withexample regenerative satellite payload 900. At operation 1302, theregenerative satellite receives a signal on the uplink. The signal maybe received at RF antenna 901, filtered using a receiver filter (e.g.,an RF filter), and downconverted. At operation 1304, the received signalis demodulated and decoded. For example, depending on the modulation andcoding of the received signal, the received signal may be demodulatedand decoded at U/L PHY 902 using any one of FEC codes 1/2, 2/3, 3/4,5/6, 7/8, 8/9, 9/10, etc., and any one of modulations formats ofAmplitude Phase Shift Keying (APSK), Quadrature Phase Shift Keying(QPSK), n/M-MPSK, other orders of Multiple Phase Shift Keying MPSK,Quadrature Amplitude Modulation (QAM), etc.

At operation 1306 a destination location field is read from a header ofa packet of the demodulated and decoded signal. The destination locationfield, in various embodiments, may provide an indication of the finalsatellite that will transmit the packet to the receiving terminal. Forexample, the destination location field may indicate a location of aground spot beam corresponding to the receiving terminal. At decision1308, it is determined if the packet needs to be routed to a differentsatellite based on the destination location field. If so, at operation1309, the packet may be routed along an ISL to another regenerativesatellite.

If the final satellite that will transmit the packet to the receivingterminal is the current regenerative satellite, at operation 1310 theregenerative satellite reads from the packet header a field indicatingthe downlink ModCod to be used when transmitting on the downlink to thereceiving terminal. After reading the ModCod, at operation 1312 theregenerative satellite encodes and modulates the downlink packet (e.g.,using D/L PHY 912) according to the desired ModCod as indicated in thepacket, and the downlink signal is transmitted at operation 1314.

FIG. 14 is a block diagram illustrating an example operation of atraffic and control processing module 1400 for a terminal of theregenerative satellite system of FIG. 8. As shown, the receiver relayforwards to transmit link adaptation module 1500 the downlink ModCodrequests received from other terminals (e.g., terminal 2 in the exampleof FIG. 14). As further described below, transmit link adaptation module1500 places these ModCod requests in headers of packets it transmits tothat terminal over a regenerative satellite network, so that the lasthop regenerative satellite knows what ModCod to use.

As described above with respect to FIG. 3, receiver link adaptationmodule 1450 may run a short-term filter and decide what ModCod it wouldlike to receive based on a Rx ACM Trajectory Table. It may send thatrequest to a Tx Packet Mux to be sent to every destination terminal withwhich the terminal is in communication such that those terminals mayidentify the correct downlink ModCod in the headers of packetstransmitted to the terminal. As mentioned above, this can be sent inseparate packets to those terminals, or as part of a transmit packet(e.g., field 1114 of FIG. 12). Module 1450 may also send the receivequality metric, having passed through the short term filter, to the Txlink adaptation module so that it can do the open loop uplink ACM ModCodcontrol/selection.

FIG. 15 is a block diagram illustrating an example operation of atransmitter link adaptation module 1500 of a terminal of theregenerative satellite system of FIG. 8. During operation, Tx ACMcontrol module 1530 uses the filtered Rx metrics and Tx ACM trajectorytable 1520 to determine what ModCod to use for transmissions on theuplink, which is indicated by the Tx relay to the Tx MAC/SLC.

Process D/L ModCod request packet module 1540 receives the ModCodrequested by a receiving/destination terminal, and saves the ModCodinformation into destination downlink ModCod Table 1510 such that the TxRelay may include it in the packet header for any packet sent to thatdestination terminal, to be acted on by the last hop regenerativesatellite when it transmits the packet on the downlink to thedestination terminal. FIG. 16 illustrates one such example destinationdownlink ModCod table 1510 that may be implemented by transmitter linkadaptation module 1500 to provide end-to-end control of downlink ModCod.For instance, with reference to the regenerative satellite system ofFIG. 8, table 1510 could be the destination downlink ModCod table ofterminal 1.

In embodiments, the disclosed systems and methods for uplink anddownlink ACM may be used in a communication system using regenerativehigh altitude platforms such as aircrafts or balloons. Particularly, theregenerative high altitude platforms may be equipped with the hardwareand software modules described above with reference to regenerativesatellites 810 a-810 c. Although the technical risk of an ACMimplementation in a regenerative high altitude system is lower than fora regenerative satellite system because high altitude platforms can belanded and upgraded, these systems are likely to be very constrained asto mass, size and power, and the disclosed systems and methods couldhelp address these constraints by placing less equipment andfunctionality on the high altitude platform.

FIG. 17 illustrates a computer system 1800 upon which exampleembodiments according to the present disclosure can be implemented.Computer system 1800 can include a bus 1802 or other communicationmechanism for communicating information, and a processor 1804 coupled tobus 1802 for processing information. Computer system 1800 may alsoinclude main memory 1806, such as a random access memory (RAM) or otherdynamic storage device, coupled to bus 1802 for storing information andinstructions to be executed by processor 1804. Main memory 1806 can alsobe used for storing temporary variables or other intermediateinformation during execution of instructions to be executed by processor1804. Computer system 1800 may further include a read only memory (ROM)1808 or other static storage device coupled to bus 1802 for storingstatic information and instructions for processor 1804. A storage device1810, such as a magnetic disk or optical disk, may additionally becoupled to bus 1802 for storing information and instructions.

Computer system 1800 can be coupled via bus 1802 to a display 1812, suchas a cathode ray tube (CRT), liquid crystal display (LCD), active matrixdisplay, light emitting diode (LED)/organic LED (OLED) display, digitallight processing (DLP) display, or plasma display, for displayinginformation to a computer user. An input device 1814, such as a keyboardincluding alphanumeric and other keys, may be coupled to bus 1802 forcommunicating information and command selections to processor 1804.Another type of user input device is cursor control 1816, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to processor 1804 and for controllingcursor movement on display 1812.

According to one embodiment of the disclosure, adaptive coding andmodulation, in accordance with example embodiments, are provided bycomputer system 1800 in response to processor 1804 executing anarrangement of instructions contained in main memory 1806. Suchinstructions can be read into main memory 1806 from anothercomputer-readable medium, such as storage device 1810. Execution of thearrangement of instructions contained in main memory 1806 causesprocessor 1804 to perform one or more processes described herein. One ormore processors in a multi-processing arrangement may also be employedto execute the instructions contained in main memory 1806. Inalternative embodiments, hard-wired circuitry is used in place of or incombination with software instructions to implement various embodiments.Thus, embodiments described in the present disclosure are not limited toany specific combination of hardware circuitry and software.

Computer system 1800 may also include a communication interface 1818coupled to bus 1802. Communication interface 1818 can provide a two-waydata communication coupling to a network link 1820 connected to a localnetwork 1822. By way of example, communication interface 1818 may be adigital subscriber line (DSL) card or modem, an integrated servicedigital network (ISDN) card, a cable modem, or a telephone modem toprovide a data communication connection to a corresponding type oftelephone line. As another example, communication interface 1818 may bea local area network (LAN) card (e.g. for Ethernet™ or an AsynchronousTransfer Model (ATM) network) to provide a data communication connectionto a compatible LAN. Wireless links can also be implemented. In any suchimplementation, communication interface 1818 sends and receiveselectrical, electromagnetic, or optical signals that carry digital datastreams representing various types of information. Further,communication interface 1818 may include peripheral interface devices,such as a Universal Serial Bus (USB) interface, a PCMCIA (PersonalComputer Memory Card International Association) interface, etc.

Network link 1820 typically provides data communication through one ormore networks to other data devices. By way of example, network link1820 can provide a connection through local network 1822 to a hostcomputer 1824, which has connectivity to a network 1826 (e.g. a widearea network (WAN) or the global packet data communication network nowcommonly referred to as the “Internet”) or to data equipment operated byservice provider. Local network 1822 and network 1826 may both useelectrical, electromagnetic, or optical signals to convey informationand instructions. The signals through the various networks and thesignals on network link 1820 and through communication interface 1818,which communicate digital data with computer system 1800, are exampleforms of carrier waves bearing the information and instructions.

Computer system 1800 may send messages and receive data, includingprogram code, through the network(s), network link 1820, andcommunication interface 1818. In the Internet example, a server (notshown) might transmit requested code belonging to an application programfor implementing an embodiment of the present disclosure through network1826, local network 1822 and communication interface 1818. Processor1804 executes the transmitted code while being received and/or store thecode in storage device 1810, or other non-volatile storage for laterexecution. In this manner, computer system 1800 obtains application codein the form of a carrier wave.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 1804 forexecution. Such a medium may take many forms, including but not limitedto non-volatile media, volatile media, and transmission media.Non-volatile media include, for example, optical or magnetic disks, suchas storage device 1810. Volatile media may include dynamic memory, suchas main memory 1806. Transmission media may include coaxial cables,copper wire and fiber optics, including the wires that comprise bus1802. Transmission media can also take the form of acoustic, optical, orelectromagnetic waves, such as those generated during radio frequency(RF) and infrared (IR) data communications. Common forms ofcomputer-readable media include, for example, a floppy disk, a flexibledisk, hard disk, solid state drive, magnetic tape, any other magneticmedium, a CD ROM, CDRW, DVD, any other optical medium, punch cards,paper tape, optical mark sheets, any other physical medium with patternsof holes or other optically recognizable indicia, a RAM, a PROM, andEPROM, a FLASH EPROM, any other memory chip or cartridge, a carrierwave, or any other medium from which a computer can read.

Various forms of computer-readable media may be involved in providinginstructions to a processor for execution. By way of example, theinstructions for carrying out at least part of the present disclosuremay initially be borne on a magnetic disk of a remote computer. In sucha scenario, the remote computer loads the instructions into main memoryand sends the instructions over a telephone line using a modem. A modemof a local computer system receives the data on the telephone line anduses an infrared transmitter to convert the data to an infrared signaland transmit the infrared signal to a portable computing device, such asa personal digital assistance (PDA) and a laptop. An infrared detectoron the portable computing device receives the information andinstructions borne by the infrared signal and places the data on a bus.The bus conveys the data to main memory, from which a processorretrieves and executes the instructions. The instructions received bymain memory may optionally be stored on storage device either before orafter execution by processor.

FIG. 18 illustrates a chip set 1900 in which embodiments of thedisclosure may be implemented. Chip set 1900 can include, for instance,processor and memory components described with respect to FIG. 18incorporated in one or more physical packages. By way of example, aphysical package includes an arrangement of one or more materials,components, and/or wires on a structural assembly (e.g., a baseboard) toprovide one or more characteristics such as physical strength,conservation of size, and/or limitation of electrical interaction.

In one embodiment, chip set 1900 includes a communication mechanism suchas a bus 1802 for passing information among the components of the chipset 1900. A processor 1904 has connectivity to bus 1902 to executeinstructions and process information stored in a memory 1906. Processor1904 includes one or more processing cores with each core configured toperform independently. A multi-core processor enables multiprocessingwithin a single physical package. Examples of a multi-core processorinclude two, four, eight, or greater numbers of processing cores.Alternatively or in addition, processor 1904 includes one or moremicroprocessors configured in tandem via bus 1902 to enable independentexecution of instructions, pipelining, and multithreading. Processor1004 may also be accompanied with one or more specialized components toperform certain processing functions and tasks such as one or moredigital signal processors (DSP) 1908, and/or one or moreapplication-specific integrated circuits (ASIC) 1910. DSP 1908 cantypically be configured to process real-world signals (e.g., sound) inreal time independently of processor 1904. Similarly, ASIC 1910 can beconfigured to performed specialized functions not easily performed by ageneral purposed processor. Other specialized components to aid inperforming the inventive functions described herein include one or morefield programmable gate arrays (FPGA) (not shown), one or morecontrollers (not shown), or one or more other special-purpose computerchips.

Processor 1904 and accompanying components have connectivity to thememory 1906 via bus 1902. Memory 1906 includes both dynamic memory(e.g., RAM) and static memory (e.g., ROM) for storing executableinstructions that, when executed by processor 1904, DSP 1908, and/orASIC 1910, perform the process of example embodiments as describedherein. Memory 1906 also stores the data associated with or generated bythe execution of the process.

As used herein, the term module might describe a given unit offunctionality that can be performed in accordance with one or moreembodiments of the present application. As used herein, a module mightbe implemented utilizing any form of hardware, software, or acombination thereof. For example, one or more processors, controllers,ASICs, PLAs, PALs, CPLDs, FPGAs, logical components, software routinesor other mechanisms might be implemented to make up a module. Inimplementation, the various modules described herein might beimplemented as discrete modules or the functions and features describedcan be shared in part or in total among one or more modules. In otherwords, as would be apparent to one of ordinary skill in the art afterreading this description, the various features and functionalitydescribed herein may be implemented in any given application and can beimplemented in one or more separate or shared modules in variouscombinations and permutations. Even though various features or elementsof functionality may be individually described or claimed as separatemodules, one of ordinary skill in the art will understand that thesefeatures and functionality can be shared among one or more commonsoftware and hardware elements, and such description shall not requireor imply that separate hardware or software components are used toimplement such features or functionality.

Where components or modules of the application are implemented in wholeor in part using software, in one embodiment, these software elementscan be implemented to operate with a computing or processing modulecapable of carrying out the functionality described with respectthereto. One such example computing module is shown in FIG. 10. Variousembodiments are described in terms of this example-computing module1000. After reading this description, it will become apparent to aperson skilled in the relevant art how to implement the applicationusing other computing modules or architectures.

Although described above in terms of various exemplary embodiments andimplementations, it should be understood that the various features,aspects and functionality described in one or more of the individualembodiments are not limited in their applicability to the particularembodiment with which they are described, but instead can be applied,alone or in various combinations, to one or more of the otherembodiments of the present application, whether or not such embodimentsare described and whether or not such features are presented as being apart of a described embodiment. Thus, the breadth and scope of thepresent application should not be limited by any of the above-describedexemplary embodiments.

Terms and phrases used in the present application, and variationsthereof, unless otherwise expressly stated, should be construed as openended as opposed to limiting. As examples of the foregoing: the term“including” should be read as meaning “including, without limitation” orthe like; the term “example” is used to provide exemplary instances ofthe item in discussion, not an exhaustive or limiting list thereof; theterms “a” or “an” should be read as meaning “at least one,” “one ormore” or the like; and adjectives such as “conventional,” “traditional,”“normal,” “standard,” “known” and terms of similar meaning should not beconstrued as limiting the item described to a given time period or to anitem available as of a given time, but instead should be read toencompass conventional, traditional, normal, or standard technologiesthat may be available or known now or at any time in the future.Likewise, where this document refers to technologies that would beapparent or known to one of ordinary skill in the art, such technologiesencompass those apparent or known to the skilled artisan now or at anytime in the future.

The use of the term “module” does not imply that the components orfunctionality described or claimed as part of the module are allconfigured in a common package. Indeed, any or all of the variouscomponents of a module, whether control logic or other components, canbe combined in a single package or separately maintained and can furtherbe distributed in multiple groupings or packages or across multiplelocations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is:
 1. A method, comprising: receiving, at a terminal, asignal on a downlink from a regenerative satellite; determining aquality of the received signal; determining an uplink modulation andcoding combination (ModCod) for uplink transmission signals from theterminal to the regenerative satellite based on the determined qualityof the received signal; and transmitting a signal on an uplink from theterminal to the regenerative satellite, wherein the signal transmittedon the uplink is modulated and encoded based on the determined uplinkModCod.
 2. The method of claim 1, wherein the terminal comprises atleast one of a gateway, a hub, and an earth station.
 3. The method ofclaim 1, wherein the terminal comprises a very small aperture terminal(VSAT).
 4. The method of claim 1, wherein determining an uplink ModCodcomprises mapping, using a table, the determined quality of the receivedsignal to the uplink ModCod.
 5. The method of claim 4, wherein thedetermined quality of the signal is a ratio of mean energy per symbol tonoise power spectral density (E_(s)N₀), wherein the E_(s)N₀ is mapped tothe uplink ModCod.
 6. The method of claim 1, wherein determining theuplink ModCod comprises mapping the determined quality of the receivedsignal to a downlink ModCod and an uplink ModCod.
 7. The method of claim6, wherein the terminal maintains downlink and uplink adaptive codingand modulation tables.
 8. The method of claim 1, wherein the determinedModCod is used to adjust a modulation scheme or forward error correctionrate applied to signals transmitted on the uplink by the terminal.
 9. Aterminal, comprising: a receiver configured to receive a signal on adownlink from a regenerative satellite; one or more processors; and oneor more non-transitory computer-readable mediums operatively coupled toat least one of the one or more processors and having instructionsstored thereon that, when executed by at least one of the one or moreprocessors, cause the terminal to: determine a quality of the receivedsignal; and determine an uplink modulation and coding combination(ModCod) for uplink transmission signals from the terminal to theregenerative satellite based on the determined quality of the receivedsignal; and a transmitter configured to transmit a signal on an uplinkto the regenerative satellite, wherein the signal transmitted on theuplink is modulated and encoded based on the determined uplink ModCod.10. The terminal of claim 9, wherein the terminal comprises at least oneof a gateway, a hub, and an earth station.
 11. The terminal of claim 9,wherein the terminal comprises a very small aperture terminal (VSAT).12. The terminal of claim 9, wherein determining an uplink ModCodcomprises mapping, using a table, the determined quality of the receivedsignal to the uplink ModCod, wherein the determined quality of thesignal is a ratio of mean energy per symbol to noise power spectraldensity (E_(s)N₀).
 13. The terminal of claim 9, wherein determining theuplink ModCod comprises mapping the determined quality of the receivedsignal to a downlink ModCod and an uplink ModCod.
 14. The terminal ofclaim 9, wherein the determined ModCod is used by the terminal to adjusta modulation scheme or forward error correction rate applied to signalstransmitted on the uplink by the terminal.
 15. A non-transitorycomputer-readable medium having instructions stored thereon that, whenexecuted by a processor, performs operations of: determining a qualityof a signal received by a terminal on a downlink from a regenerativesatellite; determining an uplink modulation and coding combination(ModCod) for uplink transmission signals from the terminal to theregenerative satellite based on the determined quality of the receivedsignal; and causing the terminal to transmit a signal on an uplink tothe regenerative satellite, wherein the signal transmitted on the uplinkis modulated and encoded based on the determined uplink ModCod.
 16. Thenon-transitory computer-readable medium of claim 15, wherein determiningan uplink ModCod comprises mapping, using a table, the determinedquality of the received signal to the uplink ModCod.
 17. Thenon-transitory computer-readable medium of claim 16, wherein thedetermined quality of the signal is a ratio of mean energy per symbol tonoise power spectral density (E_(s)N₀).
 18. The non-transitorycomputer-readable medium of claim 16, wherein determining the uplinkModCod comprises mapping the determined quality of the received signalto a downlink ModCod and an uplink ModCod.
 19. The non-transitorycomputer-readable medium of claim 15, wherein the instructions, whenexecuted by the processor, further perform an operation of using thedetermined ModCod to adjust a modulation scheme or forward errorcorrection rate applied to signals transmitted on the uplink by theterminal.
 20. The non-transitory computer-readable medium of claim 15,wherein the terminal comprises a very small aperture terminal (VSAT) orat least one of a gateway, a hub, and an earth station.